Eh normal je lah, at 5 months babies start discovering their voice and menjerit is one way dia experiment dengan sound, a few of my mum friends said their babies pun like that, especially kalau excited or want attention! The thing is, don't give in every time dia jerit kuat-kuat because it'll reinforce the behaviour, but try to figure out what she needs first (tired, hungry, uncomfortable) and respond to that instead of the volume itself lah.